oops ,, idle hands cause much trouble

[BadaBing]

In order to have some "projects" and to not be cold while doing them, I brought my carburetor and distributor home to the work bench to spiffy up for spring.
The distributor clean up went very well so I turned my attention today to the carb. Thanks to a previous thread about poor idle performance I learned that I had an idle port above the throttle plate, which we nicely clogged. a little work with a bit of monel sizing wire fixed that. Then I turned my attention to the floats, needle valve and jets. Floats were very our of wack, with the closed measurement being 1 3/8" vs 1 5/32. Most other passages and jets were clean and seemed fine, until I came to the idle jet.

The idle jet was badls stuck in its threaded hole, after working at it a while I managed to turn is about 1/2 turn out before the soft brass or bronze gave up and I lost the ability to use a screwdriver. Using a small reverse drill I drilled out the center of the jet in prep for an easy out removal. BUT even the easy out will not budge it. Im considering retaping the hole in preparation for a new idle jet. Does anyone know the tape size and pitch required?

Great, I just checked the online catalog and it seems that an "idle jet" alone is not available, anyone have a spare lying about?


Thanks

[hanleyclifford]

Bill - I have one I could send you. I'm concerned about the necessity of re tapping that hole. Seems to be an 8-32 tap.

[BadaBing]

Hanely
Thanks very much.
I did manage to find a tractor company that "claims" to have these jets in stock for under $9 each. I was worried, when I saw they are not listed on the MM online catalog, that they just are not available anywhere.

I'm confident there is enough there to retail as I did not drill it so much to reveal the threads themselves. I thought the easy out would work but what is left of the old jet is stuck fast in the body.

Do you still have my address? I'll dig your up from our last exchange and mail you a contribution.

Thanks

[hanleyclifford]

Bill - In the olden days when aluminum case transmissions were still being rebuilt in the dealerships we had a nasty lye bath that we used to clean and strip housings. I wonder if that approach might help separate the brass remaining in the housing? There isn't much room for error seating an 8-32 (if indeed I am correct about the tap size.).

[Dave Neptune]

Bill, when I get back to work I will dig up my contact on Zenith parts. I have not used them for a while however I think they're still around. I just can't remember their name. They are in the SF area of Cal.

Dave Neptune

[BadaBing]

Thanks .

It would seem a shame to trash the carb over one little little jet. Then again, the main reason I pulled it apart was because I.was not satisfied with how it idled.
Couldn't make her idle under about 1000 rpm under load and it often would die if I pushed her from partial or higher throttle to idle to quickly, like when pulling up to a dock.

[JOHN COOKSON]

Bill
Have you ever had water in your gas that made it's way into the carb and caused the brass to corrode to the aluminum?
If so did you get the watered gas under control? If you have watered gas that is the root problem and it needs to be corrected.

TRUE GRIT

[romantic comedy]

What would be the chance of filling in the jet/hole with something and drilling it out to the appropriate size?

Is it just a jet, or does it have the holes horizontal?b (emulsion tube?)

Could it be filled with solder or JB weld? Something else maybe?

[BadaBing]

John
I had quite a battle with water and gas a few seasons back. It's why I tend to be outspoken 're flushing a gas tank. I solved the source, eventually. It took replacing the fill cap. Since then I have not seen any sign of the water problem. But that could be the regional value of th I frozen in place jet. Thank.

RC. I was thinking the same thought, if it comes to that. But I think I can probably chase the threads out once we determine the appropriate tap. According to the exploded view it is just a jet so I probably haven't killed it.

[Al Schober]

Bada,
I think I bought some Zenith carb parts (including the idle jet) from a place selling parts for Gravely tractors. As I recall (CRS kicking in) their prices were quite reasonable.

[JOHN COOKSON]

If all else fails and it looks like write off try heat + torque + impact to remove the idle jet. Something like heat the area up toasty warm and then tap on the easy out while you twist it with a wrench.

TRUE GRIT

[hanleyclifford]

Before attempting to remove that idle jet (or any jet for that matter), it really, really pays to take the time on a bench grinder to modify a screw driver to make a perfect fit in the jet. Also, it is not necessary to crank the jet into it's seat - just a light twist to seat is all that is required; trust me, the jet will not fall out.

[JOHN COOKSON]

If the jet comes loose but is still tight twist counter clockwise and clockwise as you remove it. This will help loosen it. This sounds counter intuitive but it does work.
After you get the jet out I hope there is enough aluminum left to tap. Aluminum is the sacrificial metal with brass. It may be necessary to fix the new jet in by some other means. Maybe epoxy? I don't know if epoxy is fuel poof or not.

TRUE GRIT

[BadaBing]

All great advise. But. Even though it was a correct screw driver size and I thought I was careful I still managed to twist off the top portion of the jet. So I drilled it out to almost the threads.
N e x t step is to chase the threads

[hanleyclifford]

Bill - I need to know which type you have (from the picture). BTW, thread seems to me more like 8-32, which I do not have.

[Al Schober]

I've got a brand new jet just like the one on the left, which I think is the idle jet. Thread is an odd ball size. Measures .150", with 32 tpi. It's not #8, as a #8 nut almost swallows it! Yet too big for a #6. Is there a 3.8mm thread? I know I sure don't have a tap like that in my collection.
Oh yeah, the hole size seems to be just over .020" - maybe .022"?
Correction: The thread on that jet is #8-32. The nut I tried was in my #8 bin, but was actually a #10.

[hanleyclifford]

Originally Posted by Al Schober

I've got a brand new jet just like the one on the left, which I think is the idle jet. Thread is an odd ball size. Measures .150", with 32 tpi. It's not #8, as a #8 nut almost swallows it! Yet too big for a #6. Is there a 3.8mm thread? I know I sure don't have a tap like that in my collection.
Oh yeah, the hole size seems to be just over .020" - maybe .022"?

Thanks for the measurement help, Al. I knew something was fishy when I couldn't get the #6 nut on (but not by much). Odd ball sizes include metric and British pipe, straight and tapered, and probably some other stuff I don't know about. The two small jets came out of idle holes. Obviously there was a change somewhere along the line. For size comparison the big jet in the picture is the well vent jet.

[ndutton]

Suggest you contact Tom Vandiver (2dogsfishin) on the forum and see what he has available.

[BadaBing]

Hanley.
I can't tell at the moment which of the 2it is. While drilling it it seems I needed to drill deeper than I would have expected to drill through the smaller one. However, looking at the mm catalog picture for a carb rebuild.kit it seems that there is nothing in the kit like.the.longer of the 2 jets you have shown. Perhaps they are interchangeable?

The thread size and type is a challange. Ken at MM couldn't advise and.didn't know.who could.

I'm beginning to think that this is a job for JB weld. Nothing to loose at this.point.

[BadaBing]

Neil.
Would you mind sending me Tom's number in a PM? I thought he had sold his remaining stock but saw a listing on eBay for A4 parts that looked like his.

[ndutton]

On the blue header bar on this page you'll see "Community." Click on that, slide down to "Members List" and click. Scroll down to 2dogsfishin and to the right you'll see an email link. There you go.

[hanleyclifford]

Originally Posted by BadaBing

Hanley.
I can't tell at the moment which of the 2it is. While drilling it it seems I needed to drill deeper than I would have expected to drill through the smaller one. However, looking at the mm catalog picture for a carb rebuild.kit it seems that there is nothing in the kit like.the.longer of the 2 jets you have shown. Perhaps they are interchangeable?

The thread size and type is a challange. Ken at MM couldn't advise and.didn't know.who could.

I'm beginning to think that this is a job for JB weld. Nothing to loose at this.point.

Based on my observation of the castings from which each jet was taken, the shorter jet is the latest type so I'm going to send you that jet and it's housing. I've got a milk crate full of this stuff. We'll just take our best shot and see how it fits. But if you have only one carb on hand I think it might still be a good move to buy the Moyer rebuild kit and keep it on board, especially if you have cruising plans.

[ndutton]

Bill, what do you plan to do with JB Weld, glue in a replacement jet? This sounds to me like if it even works it will be a constant worry. If successful I'd consider this a temporary solution at best.

[BadaBing]

Here is an update on my progress, or lack of progress.

After a close examination I am sure that my idle jet WAS the short version of the two Hanley shared the picture of.

The helpful folks at MM dont know that size and thread is needed to retap or chase the threads.

I spent some time searching Google for Zenith 68 Carb and located a company GT Enterprises. GT Enterprises sells a new reversed version of the zenith 68 carb and seem to be quite knowledgeable about them as well as selling all sorts of parts for them, They are a Gravely Tractor parts supplier.

I called them just a little while and spoke with Todd, . Todd said they sell a lot of parts to A-4 owners. after giving him my carb number from the tag, 13355 K he said he would put a call into the folks at Zenith and ask them about parts for my carb. I asked he check with Zenith re a proper tap to re-tap my idle jet hole. He said he didnt know exactly what the size is BUT that it IS a metric size.



More news to follow as new fact arise.

gtgravelyparts.com

On another note. Apparently Gravely Tractors use a version of a zenith model 68 carburetor. Im thinking of Dave's previous explanation of our carburetors actually being to large for our direct drive applications. Because the Gravely engines are smaller (up to 7.6 hp ) than our A4 engines Im wondering if the venturi (sp?) in the model 68 carburetor they use may be machined differently.

for clarity sake I am adding the excellent post by Dave Neptune about our carburetors. I dont know if we have a hall of fame section for outstanding posts but I would nominate this one if we do.


Carbs~FII~&the A--4 an opin


" Neil, yes I do mean that the carb is bigger than necessary. It was a very common thing way back as there were not that many to ""CHOOSE FROM" that met the engine manufactures criteria, so they choose something close. It is not a bad thing, it is just not as efficient across the power band. This same late model carb is capable of developing 70hp on larger engines.

A good rule for "economy" is to run a bit smaller than absolutely necessary as the carb will work across it's "designed" power band. Much can be done inside the carbs themselves which is why you will see many part numbers on the same "basic" carb. The differences are inside as the transfer bleeds and the metering will be calibrated for the application. You can find many "application part numbers" for our Zeniths. It is the same carb just calibrated differently for it's application. All of the different part numbered carbs will work on just about everything that it will bolt up too but efficiency comes to play.

We are running a "load duty" application so we want the power band to be at as close to WOT as possible when the engine is working under loads. This puts the carb well into the "last of the power stage" of the carb where it will be most efficient in getting a good mix to the cylinders. This good mix happens at higher velocities through the carb at it's upper limits. Everything below that accept base IDLE is a compromise of proper mix. This is where FI becomes more efficient, mostly on the in between RPM ranges. I have sat in on tests with the same engine ( Niel, it was the owners red Camero where one of your friends works) on a dyno using FI and carburation. They both idled fine and the carb actually made the most power and I think it was around 6hp on a 500 horse engine. On the track the FI was clearly much faster as it had a power advantage coming out of turns via the efficiency and mix control in the mid-ranges. On the drag strip they were virtually the same and being faster was a matter of the run being driven.
Take Hanley's ""Xboxes" approach. He can vary the spark intensity and with his O2 sensor he can tweak his adj jet to a good mix. The fact that he can do this points out the inefficiencies of a GOOD carb our Zeniths.
The 36 hp VW carb would be a good "power match" for the A-4 however mounting and sequencing of the internals may take a tweak or two.
The Zeniths have a replaceable VENTURI much like Webbers and if a smaller one could be found and the data could be extracted from Zenith on the internals we would be better off.
I have found some inequities in many of the A-4 carbs I have done for A-4's over the years. I have found after market jets that do not follow Zeniths actual openings and a few different emulsion tubes as well. The original combination provided to Universal has been somewhat bastardized and the after market jets add to the problems at the rebuilders.
Now if we were to develop a smaller carb and really got it dialed in or it's mix across the power band it would probably take at least 10 hours of running to measure any gains in overall economy and this is pretty much the same when trying to convert to FI. It just is not worth the effort and investment to go FI for so little gain in a load duty application.
A good well balanced and set Zenith is going to be hard to beat unless a major investment is made and it just is not worth the effort in my opin.
I have massaged the internals of my carb and have only seen a few with the same sequencing in the emulsion wells, these were all on very old carbs that could be stated to be still original.

My carb has been on and not removed now for 5 years running E-regular gas. It runs great and my economy is right there with some of the best claims I have seen on this site. I put a lot of hours on so my fuel is mostly fresh and my tank is clean. My Racor is now at least 10 years old and the filter has not been touched in that time. I do run a polishing filter before the carb and I do not remember when it was last changed out. I use no additives and I only get my gas from a gas station not a marina gas dock!!

We should also notice that the more a boat is run the less trouble we have. The engines that are started just to get out of the marina and barely ever even warmed up are the ones with seemingly fuel related problems especially regarding contamination.

Most A-4 carb problems are related to an internal air leak (the matching of the halves), improper float setting (the Zenith is very sensitive to float level and not the angle of the mounting as it is center fed) and not getting everything out of idle and mid range passages when cleaning.

OUT "

[JOHN COOKSON]

Originally Posted by BadaBing

On another note. Apparently Gravely Tractors use a version of a zenith model 68 carburetor. Im thinking of Dave's previous explanation of our carburetors actually being to large for our direct drive applications. Because the Gravely engines are smaller (up to 7.6 hp ) than our A4 engines Im wondering if the venturi (sp?) in the model 68 carburetor they use may be machined differently.

I always wondered if the same thing: if the same model 68 carb was used for many different engines the only difference being than the jets, ventures ect were changed inside the carburetor to match the engine. I don't really know that much about it though.
Dave N. Are you logged on?

TRUE GRIT